T 1.5 - 1.9 Flashcards
Physical processes that volcanoes cause
- lava flows
- pyroclastic flows
- ash falls
- gas eruptions
- secondary hazards - lahars, jökulhlaup
What are lava flows and how are they caused?
- molten magma on the earths surface is so hot, it flows
- viscosity determined by the amount of silicon dioxide
- buildings can be burnt and covered if it is running
- 1977: lake wall collapsed and lava drained in 1 hr, across 9km, swallowing villages while people were asleep
Gas steam emissions from volcanic eruptions:
- h20 vapour: rainfall events, then potentially lahars
- steam escapes though geysers
- so2 forms very fine particles that get into the stratosphere, also causes acid rain which corrodes buildings and affects vegetation
- fluorine gas is poisonous in high conc. and contaminated farmland or water supply
What are pyroclastic flows and how are they caused?
- frothing bubbles of molten magma in the vent, burst explosively to eject a dense mixture of hot gases and pyroclastic material, eg glass, pumice, ash
- can reach temperatures of up to a 1000
- move rapidly down side of volcano up to 700km/h
- leave behind volcanic deposits ( can dam rivers)
How are ash falls caused and what are they?
- carried into the atmosphere, potentially even trans boundary
- most fall locally, causing roofs to collapse, breathing difficulties for people and animals, bury crops
- disrupts flights paths of planes
How are lahars caused and what are they?
- water mixed with volcanic deposits, flowing rapidly along existing valleys
- could be caused by heavy rain, or maybe volcanic ash has has created humid air, condensation, clouds and rain
- very fast (60kmh) carry large amounts of material
Impacts of Mountain Nyiracongo eruption
- major eruptions in 1977, 2002, 2021
- 2km wide continuous lava lake
- responsible for 40% of Africa’s volcanic eruptions
- shield volcano
2002 - 147 killed, 400k evacuated
Eykafjallajokull eruption 2010
- single eruption divided into many phases
- 14th April, relatively explosive eruption (4 on VEI)
- situated 200m under glacial ice, where melt water caused two things: rapidly vaporising water, rapid lava cooling created cloud of abrasive glass rich ash
- but deaths = 0
Social/ human impacts of Eykafjallajokull eruption
- cancelled sports, music and arts events
- localised health effects around south Iceland due to abrasive ash
- increased regional traffic for land based travel
- cancelled/postponed political events
Economic impacts of eykafjallajokull eruption
- European economy lost 5 billion
- African economies lost as much as 65 million
- loss for airlines ($1.1 billion)
- knock on effect from cancelled events (eg, MotoGP in Japan)
Regional significance of eykafjallajokull eruption
- ash cloud reached as far as northern Italy, meaning any flights to and from Europe were affected
- increased in land based travel so train prices and road traffic rose
- however reduced air and noise pollution recorded around Europe
Global significance of eykafjallajokull eruption
- Japan MotoGP suffering
- Kenyan flower industry lost 2 million
- New Zealand fish farmers still were winners as they could have more domestic demand
Land use zoning
- keeping residential and commercial zones away from active dormant volcanoes
- easier with shield volcanoes
- hard because of soi fertility
Hazard resistant design
- retrofit buildings
- cross bracing
but this is expensive on a national scale and requires government legislation
Engineering defences
- sea walls and mangroves to absorb wave energy
- back up utility plans for hospitals and police stations
- drain craters to prevent lahars
Diversion of lava flows
- spray sea water to solidify lava and create basalt rock to diverse lava flows
Remote sensing
- monitor gas emissions
- cloud monitoring
- monitor fault line staring
- tilitometers measure ground deformation
Hawaii earthquake facts and figures
- early may 2018
- magnitude 6.9
- 24 fissures
- 2000 people evacuated, with damage to electricity generation
- $800m damage
How they become disasters - local variables
- distance from source (waves lose energy longer you go)
- offshore bathymetry (shallow or deep)
- coastal topography and geology
- extent vertical fault displacement
Benioff zone
- area with height seismic activity/ slab moving downward
- speed and movement of rock produces earthquake
- locked faults are significant concern
- slab builds tension due to frictional resistance, until they release a huge amount of energy in the form of an earthquake
How tectonics could affect landslides
- focal depth (changes MMS)
- change amounts of folding (steeper)
- change lava type
- hydration melting - more explosive andesitic lava
Stresses at a plate boundary
- angle of slope
- rainwater/ saturation
- vibration
- earthquakes
- sea/cliff erosion
Strengths at a plate boundary
- lubricant layers
- tree vegetation roots
- consolidation of material
- porosity of soil
Chile - The Andes 🇨🇱
- convergent plate boundary
- Anzac plate below the South American plate
- major EQ and volcanic eruptions
- EQ can trigger avalanches, rock avalanches and landslides
Punta Cola avalanche:
Strength - tree bunds land together giving it resistance
Stress - water doing hydraulic action breaking the land cashing a landslide
Characteristics of a shield volcano
- constructive plate boundary
- divergence
- lower silicates and gas content in magma
- continuous eruption
- runny, basaltic lava, gentle slope, shorter volcano
Characteristics of a composite volcano
- destructive plate boundary
- subduction
- higher silicates and gas content in magma
- longer dormancy, pressure build up
- explosive eruption, gas and material
- viscous andesitic lava
- steep sided tall volcano
So overall, how are landslides formed at destructive plate boundary?
- one plate is folded up
- steeper gradient
- increased gravity in this plate which can increase likelihood of landslides
- magma can melt the plate = landslides
1.8 overall
Tsunamis form and are shaped by coastal morphology e.g Indian Ocean
Keychain for tsunami
• Destructive plate boundary
• Subduction zone
• Earthquake
• Megathrust fault – water displacement
• Wave… which is fine until the sea-bed shelves
• Then friction drags at the bottom of wave as bed shelves
• Wave frequency / amplitude changes and grows before hitting land
• Backwash out, swash in (wave crash)
